Conventional backlight devices that are used for liquid crystal display devices include a side-lighting type backlight device in which a light source is disposed so as to face the side surface of a light guide plate, a direct-lighting type backlight device in which a light source is disposed directly below a liquid crystal panel, and the like. The side-lighting type backlight device is used for small and medium-sized liquid crystal display devices and liquid crystal display devices that require thin-profile, in particular. The direct-lighting type backlight device is used for large monitors, televisions, and the like. In the past, the light source of these backlight devices was mainly made of cold-cathode fluorescent lamps (CCFL), but recently, in view of environmental issues, the CCFLs have been replaced by LEDs that use less power and contain no mercury.
Patent Document 1 shown in FIG. 8 is an example of the side-lighting type backlight device that uses LEDs as the light source thereof. Patent Document 1 describes a side-lighting type backlight device that has a plurality of light sources, in which four chip-type LEDs 9a to 9d, for example, are provided on a light incident surface 71 of a light guide plate 7. In light source facing portions of the light incident surface 71 (preferably two ends of the light incident surface 71), which face at least the chip-type LEDs 9a and 9d at the opposite ends, inclined surfaces 7a and 7b are formed, and with these inclined surfaces 7a and 7b, the chip-type LEDs 9a and 9d are disposed such that optical axes L1 and L2 thereof are directed toward the center of the light guide plate 7. In Patent Document 1, with this configuration, light emitted from the respective light sources are distributed uniformly in the entire light guide plate, thereby providing the illuminating light with enhanced uniformity to a liquid crystal display element.
Structures and types of a typical chip-type LED are explained with reference to FIG. 9. A chip-type LED 9 includes a semiconductor light-emitting element (not shown) that has an n-type semiconductor layer, a p-type semiconductor layer, and an active layer sandwiched therebetween and that is packaged in a package 15 and connecting terminals 16 (anode and cathode) that are used to connect the semiconductor light-emitting element to a circuit board, thereby supplying power, for example. Further, the package 15 has a light-emitting surface 14 where a lens that adjusts directional characteristics of illuminating light is provided. The chip-type LEDs are categorized into two types, a top-emitting type and a side-emitting type, depending on where the light-emitting surface 14 is located with respect to the package 15.
In the top-emitting type (top view type) shown in FIG. 9(a), the light-emitting surface 14 is provided on the top surface of the package 15, and light is emitted in a direction perpendicular to a mounting surface 91 that faces the connecting terminals 16. The top-emitting type LED 9 has advantages such as higher brightness and longer life. Also, because the illumination direction is perpendicular to the mounting surface 91, this type is mainly used for the direct-lighting type backlight device. Specifically, by disposing a substrate having the chip-type LED 9 mounted thereon below the bottom surface of the light guide plate 7 such that the mounting surface 91 becomes parallel with the light guide plate 7, the light-emitting surface 14 of the chip-type LED 9 faces the light incident surface, which is the bottom surface, of the light guide plate 7.
On the other hand, in the side-emitting type (side view type) shown in FIG. 9(b), the light-emitting surface 14 is provided on the side surface of the package 15, and light is emitted in a direction parallel with the mounting surface 91. Because Patent Document 1 and conventional side-lighting type backlight devices are configured such that light is emitted to the light incident surface 71 that is provided on the side surface of the light guide plate 7, this side-emitting type LED 9 is employed therein. Specifically, by disposing a substrate having the side-emitting type LED 9 mounted thereon near the side surface of the light guide plate 7 such that the mounting surface 91 becomes parallel with the light guide plate 7, the light-emitting surface 14 of the chip-type LED 9 faces the light incident surface provided on the side surface of the light guide plate 7. With this side-emitting type LED 9, when improving the uniformity of the illuminating light in the manner described in Patent Document 1 shown in FIG. 8, the light-emitting surfaces of the LEDs 9 can be easily arranged so as to face the inclined surfaces 7a and 7b of the light emitting surface 71 by turning the LEDs 9 horizontally on the substrate.